Reference to the chart in figure 1-35 will show that banking
an airplane just over 75° in a steep turn increases the stalling speed
by 100 percent. If the normal unaccelerated stalling speed is 45 knots,
the pilot must keep the airspeed above 90 knots in a 75° bank to prevent
sudden entry into a violent power stall. This same effect will take place
in a quick pullup from a dive or maneuver producing load factors above
1 G. Accidents have resulted from sudden, unexpected loss of control, particularly
in a steep turn near the ground.

Reference to the chart in figure 1-35 will show that banking an airplane
just over 75° in a steep turn increases the stalling speed by 100 percent.
If the normal unaccelerated stalling speed is 45 knots, the pilot must
keep the airspeed above 90 knots in a 75° bank to prevent sudden entry
into a violent power stall. This same effect will take place in a quick
pullup from a dive or maneuver producing load factors above 1 G. Accidents
have resulted from sudden, unexpected loss of control, particularly in
a steep turn near the ground.

Figure 1-35.—Stall speed chart.

The maximum speed at which an airplane can be safely stalled is the design
maneuvering speed. The design maneuvering speed is a valuable reference
point for the pilot. When operating below this speed, a damaging positive
flight load should not be produced because the airplane should stall before
the load becomes excessive. Any combination of flight control usage, including
full deflection of the controls, or gust loads created by turbulence should
not create an excessive air load if the airplane is operated below maneuvering
speed. (Pilots should be cautioned that certain adverse wind shear or gusts
may cause excessive loads even at speeds below maneuvering speed.)

Design maneuvering speed can be found in the Pilot’s Operating Handbook
or on a placard within the cockpit. It can also be determined by multiplying
the normal unaccelerated stall speed by the square root of the limit load
factor. A rule of thumb that can be used to determine the maneuvering speed
is approximately 1.7 times the normal stalling speed.
Thus, an airplane which normally stalls at 35 knots should never be
stalled when the airspeed is above 60 knots (35 knots x 1.7 = 59.5 knots).

A knowledge of this must be applied from two points of view by
the competent pilot: the danger of inadvertently stalling the airplane
by increasing the load factor such as in a steep turn or spiral; and that
intentionally stalling an airplane above its design maneuvering speed imposes
a tremendous load factor on the structure.

Effect of Speed on Load Factor

The amount of excess load that can be imposed on the wing depends
on how fast the airplane is flying. At slow speeds, the maximum available
lifting force of the wing is only slightly greater than the amount necessary
to support the weight of the airplane. Consequently, the load factor should
not become excessive even if the controls are moved abruptly or the airplane
encounters severe gusts, as previously stated. The reason for this is that
the airplane will stall before the load can become excessive. However,
at high speeds, the lifting capacity of the wing is so great that a sudden
movement of the elevator controls or a strong gust may increase the load
factor beyond safe limits. Because of this relationship between speed and
safety, certain “maximum” speeds have been established. Each airplane is
restricted in the speed at which it can safely execute maneuvers, withstand
abrupt application of the controls, or fly in rough air. This speed is
referred to as the design maneuvering speed, which was discussed previously.

Summarizing, at speeds below design maneuvering speed, the airplane
should stall before the load factor can become excessive. At speeds above
maneuvering speed, the limit load factor for which an airplane is stressed
can be exceeded by abrupt or excessive application of the controls or by
strong turbulence.

Effect of Flight Maneuvers on Load Factor

Load factors apply to all flight maneuvers. In straight-and-level
unaccelerated flight, a load factor of 1G is always present, but certain
maneuvers are known to involve relatively high load factors.

• Turns—As previously discussed, increased load factors are a
characteristic of all banked turns. Load factors become significant both
to flight performance and to the load on wing structure as the bank increases
beyond approximately 45°.

• Stalls—The normal stall entered from straight-and-level flight,
or an unaccelerated straight climb, should not produce added load factors
beyond the 1G of straight-and-level flight. As the stall occurs, however,
this load factor may be reduced toward zero, the factor at which nothing
seems to have weight, and the pilot has the feeling of “floating free in
space.” In the event recovery is made by abruptly moving the elevator control
forward, a negative load is created which raises the pilot from the seat.
This is a negative wing load and usually is so small that there is little
effect on the airplane structure. The pilot should be cautioned, however,
to avoid sudden and forceful control movements because of the possibility
of exceeding the structural load limits.

During the pullup following stall recovery, however, significant
load factors are often encountered. These may be increased by excessively
steep diving, high airspeed, and abrupt pullups to level flight. One usually
leads to the other, thus increasing the resultant load factor. The abrupt
pullup at a high diving speed may easily produce critical loads on structures,
and may produce recurrent or secondary stalls by building up the load factor
to the point that the speed of the airplane reaches the stalling airspeed
during the pullup.

• Advanced Maneuvers—Spins, chandelles, lazy eights, and snap
maneuvers will not be covered in this handbook. However, before attempting
these maneuvers, pilots should be familiar with the airplane being flown,
and know whether or not these maneuvers can be safely performed.